This is good for developers. But we know Apple will drag their feet on rolling this out for as long as they're legally able to per their statement that they will need time to figure out the "complex and rapidly evolving legal, technological, and economic issues" that the update would cause.
I don't know, man. If I'm given the choice to pay via the App Store or via, ostensibly, an unknown payment system - I'm going for the App Store 100% of the time.
I'm not sure how that is good for developers.